Minimum requirements to make another unit

[Kelly Conrad]

I can't seem to find this anywhere, so I'm hoping someone could have some insight.

Are there minimum requirements to add another unit to a building? So say we have a home that's a duplex, what would need to happen to create a triplex, assuming it would be in the basement?

I'm guessing it has to be within the existing home, has to have a separate entrance, a bathroom, bedroom, living room and kitchen? Does there have to be a space requirement for the unit as a whole, different rooms? I look forward to your responses!